Physical properties measurements at Site 1116 were limited by low core recovery, and consequently, the physical properties data set for the site is sparse. Physical properties evaluation included nondestructive measurements of bulk density, bulk magnetic susceptibility, and natural gamma ray on unsplit core using the MST. Discrete measurements of longitudinal and transverse P-wave velocities and index properties were collected on split cores. Depending on the level of sediment induration, thermal conductivity was measured from unconsolidated whole cores, discrete rock slices, or conglomerate clasts. Poor recovery and fragmented sections in Cores 180-1116A-1R, 5R through 8R, and 11R through 12R precluded use of the MST at these locations. Further, it was not possible to measure compressive strength and undrained shear strength because of the well-lithified nature of the recovered sediment.
Bulk densities at Site 1116 were derived from both gamma-ray attenuation porosity evaluator (GRAPE) measurements conducted on unsplit cores and discrete density measurements on sediment and rock samples (Table T8; also in ASCII format in the ASCII TABLES directory). A full compilation of GRAPE data is presented in ASCII format with the MST measurement data set on the accompanying LDEO CD-ROM. Composite profiles of these independently derived bulk densities indicate a fair agreement between the two, with the discrete measurements tending to define an upper boundary of the GRAPE densities (Fig. F35A).
One exception occurs for Core 180-1116A-3R, in which the index properties estimate is ~3.1 g·cm-3. This density, checked and remeasured, corresponds to an isolated sample of calcite-cemented (checked with XRD analysis), low porosity, high grain density, fine-grained sandstone and is not representative of lithostratigraphic Unit I (see "Lithostratigraphic Unit I"). There is no obvious explanation for this outlier value. GRAPE underestimation of bulk density may be related to small core diameters produced by RCB drilling. Corrections were attempted at a previous site (see "Density and Porosity" in the "Site 1109" chapter), but could not fully account for the discrepancy. Because of these discrepancies and the large scatter in the GRAPE data, our discussion will focus primarily on the discrete bulk density measurements.
In contrast to bulk densities obtained from other Leg 180 sites, the near-surface bulk density at Site 1116 is relatively high, having a value of ~2.15 g·cm-3 at depths of 7-8 mbsf (Fig. F35A). Bulk densities remain approximately constant over the length of the borehole with the average at 2.30 g·cm-3, and show no obvious correlation with either the lithostratigraphic units or their boundaries. The relatively high near-surface densities imply removal of the uppermost sediment, an implication supported by the absence of Pleistocene deposits (see "Biostratigraphy").
Grain densities average 2.73 g·cm-3 from the seafloor to 152 mbsf (Fig. F35B). An explanation for the scatter associated with estimates at 16 and 25 mbsf is unclear, but may relate to experimental or instrument-related errors. As with bulk densities, the grain densities are approximately constant irrespective of the lithology recovered (Fig. F35B).
At Site 1116, porosities show a large degree of scatter, ranging from 10% to 41%, with an average of ~26.5% (Fig. F36A). Porosity values throughout the entire profile are low, as illustrated by near-seafloor values of 33% and 11%, and do not show the usual negative exponential variation of porosity with depth often seen in normally compacting sediments (Athy, 1930). As indicated in Figure F36A, porosities lower than 15% generally correlate with isolated samples of carbonate-cemented sediments (see "Depositional History"). The anomalous near-seafloor porosities may reflect an environment in which sediment deposited on what is now the top of Moresby Seamount has since been eroded. This hypothesis is consistent with (1) the absence of calcareous nannofossil Subzones NN21B to NN19A at the top of the borehole, which indicates a hiatus in the sedimentary record of at least 1.95 Ma (see "Biostratigraphy"); and (2) the interpretation of reflection seismic data suggesting the truncation of reflectors.
To estimate the thickness of sediment that may have been eroded, a least squares exponential curve was fit to porosity data with the extreme low values removed (Fig. F36B). The curve fitting predicts a surface porosity of 31.6% and a compaction decay constant of 0.0009 m-1. Significant data scatter and the small number of observations result in a poor correlation coefficient of 0.3 (Fig. F36B). Extrapolating the exponential porosity-depth relationship to the presumed paleosurface, assuming initial surface porosities of 75% (i.e., seafloor porosities from previous Leg 180 sites), implies that ~960 m of sediment has been removed from the upper stratigraphic units at this site. This estimate is in broad agreement with a comparison of porosity-depth relationships from other Leg 180 sites (e.g., Sites 1109 and 1115). It is important to stress that because of the limited data set and the low correlation coefficient, the erosion estimate is poorly constrained.
Compressional wave, or P-wave, velocity was measured on split cores using the PWS3 contact probe system. All cores were sufficiently indurated to prepare ~10-cm3 cubes, thereby allowing for velocity measurement in the transverse (x and y) and longitudinal (z) directions. The PWS data are presented in Table T9 (also in ASCII format in the ASCII TABLES directory). Most of the Hole 1116A cores consisted of indurated sediment, with the exception of Cores 180-1116A-5R through 8R, which consisted primarily of conglomerate clasts removed from the matrix material. The recovery of conglomerate clasts provided an opportunity to characterize the transverse (x) direction for a variety of igneous rock types. It should be noted, however, that the original orientation of the clasts is unknown because of possible rotation within the core barrel. Clasts consisted of vesicular, porphyritic, and amygdaloidal basalts, along with andesites and dolerite (see "Lithostratigraphy").
The velocities show a large degree of scatter ranging from 2400 to 5500 m·s-1 (Fig. F37). Some of this scatter relates to calcite-cemented sandstone and siltstones of lithostratigraphic Units I and III (see "Lithostratigraphic Unit I," and "Lithostratigraphic Unit III") and the selected sampling of conglomerate clasts from lithostratigraphic Unit II (see "Lithostratigraphic Unit II"). Near-surface velocities obtained in the upper 10 m of the borehole range from ~2200 to ~2800 m·s-1, which are significantly higher than expected for shallow-marine sediments. However, these higher velocities are consistent with the low near-surface porosities. Evaluation of the triaxial velocity measurements indicates that transverse velocities are systematically faster than longitudinal velocities (Fig. F38A), with velocity anisotropies ranging from 0.5% to ~9% (Fig. F38B).
Thermal conductivity measurements were conducted on split cores from Site 1116 using the half-space method. The thermal conductivity values presented in Figure F39 are averages of repeat measurements in the same interval. A full compilation of the data is presented in Table T10 (also in ASCII format in the ASCII TABLES directory).
Thermal conductivity values in sediments at Site 1116 are likely governed by pore space and composition of clasts. Thermal conductivity measurements for Site 1116 show considerable variation, ranging between 1.0 and 2.2 W·m-1·ºC-1 (Fig. F39). Generally, low-porosity calcareous sandstones from lithostratigraphic Units I and III are associated with conductivities higher than 1.8 W·m-1·ºC-1. Otherwise, no direct correlation exists between lithostratigraphic units and thermal conductivities.
At Site 1116, estimates of magnetic susceptibility were routinely obtained as part of the MST measurements. The quality of magnetic susceptibility data is often poor in RCB-cored boreholes, commonly because of a reduced core diameter and drilling induced fracturing. At Site 1116, the low recovery throughout the succession also limits the degree of interpretation that can be placed on the magnetic susceptibility data. The full data set can be found as part of the MST compilation in ASCII format on the accompanying LDEO CD-ROM.
Because of poor recovery magnetic susceptibility data were obtained only from 5-25, 65-75, and 100-152 mbsf (Fig. F40A). Given that lithostratigraphic Units I and III consist of a monotonous assemblage of sandstone and siltstone couplets (see "Lithostratigraphic Unit I" and "Lithostratigraphic Unit III"), there is no obvious relationship between the general susceptibility trends and either the lithology and/or the grain-size distribution. However, isolated susceptibility peaks often correlate with volcaniclastic sandstone layers (see "Lithostratigraphy").
Natural gamma-ray (NGR) emissions were recorded on cores from Site 1116 as part of continuous MST measurements. A full compilation of NGR values is presented with the MST measurement data set in ASCII format on the accompanying LDEO CD-ROM.
Irregular core recovery makes it difficult to define trends within the NGR data (Fig. F40B). Nevertheless, comparing the magnetic susceptibility with NGR on a core-by-core basis suggests that there is a general inverse relationship between the two. For example, a relatively high amplitude magnetic susceptibility associated with Core 180-1116A-3R (16.20-17.09 mbsf) correlates with a low-amplitude NGR count (Fig. F40B). In contrast, the low magnetic susceptibility for Core 180-1116A-18R (149.30-152.43 mbsf) correlates with a NGR high. This inverse relationship suggests that the clastics containing the magnetic mineralogy are distinct from those clastic units containing radiogenic components. As with the magnetic susceptibility, the general NGR trends do not correlate with either the lithology or the grain-size distribution.